Abstract/Details

Separating environmental effects from fishing impacts on the dynamics of fish populations of the southern California region


2006 2006

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Abstract (summary)

Disentangling environmental variability from fishing effects on the dynamics of fish populations is essential for sound fisheries management. This is an important component of ecosystem approaches to fisheries. Toward this goal, I compare exploited with unexploited species living in the same environment. Using greater than 50-year long larval fish time series collected in the California Cooperative Oceanic Fisheries Investigations (CalCOFI) from the southern California region, I consider fishing as a treatment effect in a long-term ecological experiment. I construct an "expert-knowledge classification system" to categorize southern California fish species collected during the CalCOFI surveys into communities based on the habitat affinities of adults (coastal, coastal-oceanic, and oceanic), and incorporate their life history traits, phylogeny, and status of exploitation into analyses.

Fisheries exploitation occurs only in the coastal and coastal-oceanic communities. Within these communities, very few species exhibit a significant linear correlation with environmental variables, and exploited species are not more responsive to climate than unexploited species. However, the long-term variability in the abundance of exploited species is higher than that of unexploited species, after accounting for life history effects, phylogeny, and a changing environment. The increased variability of the exploited populations is likely caused by fishery-induced truncation of age-structure, which reduces the capability of populations to dampen the effects of environmental variability. This inference is substantiated by analyzing age or length composition in catch data for the exploited species used in this study, which clearly indicate a declining trend in average age or length through time. Furthermore, the latitudinal distributions of exploited species are more responsive to climate changes than those of unexploited species, suggesting that fishing may reduce the resilience of fish populations facing environmental variation. The reduced resilience may be caused by fishery-induced truncation of age-structure or constriction of spatial distributions.

My results indicate that fishing is likely to magnify uncertainty of fish populations and therefore, increase the probability of dramatic shifts of the populations facing environmental variations. A precautionary management approach is warranted not only because of normal uncertainties associated with estimates of stock size but because fishing magnifies population variability. Therefore, in addition to maintaining total viable biomass, management strategies should be implemented to conserve fish population structures in order to prevent fishing from increasing population variability.

Indexing (details)


Subject
Oceanography;
Aquaculture;
Fish production
Classification
0416: Oceanography
0792: Aquaculture
0792: Fish production
Identifier / keyword
Biological sciences; California; Fishing
Title
Separating environmental effects from fishing impacts on the dynamics of fish populations of the southern California region
Author
Hsieh, Chih-hao
Number of pages
191
Publication year
2006
Degree date
2006
School code
0033
Source
DAI-B 67/03, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780542587092, 0542587092
Advisor
Sugihara, George; Ohman, Mark D.
University/institution
University of California, San Diego
University location
United States -- California
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3210008
ProQuest document ID
305338514
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/305338514
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